Cocaine sensitization is a progressive and long-lasting enhancement of the motor stimulant effect induced by a subsequent cocaine challenge. The goal of this work is to elucidate if the persistent activity of PKM? in the VTA and NAc sustains the development and expression of cocaine sensitization. There are three specific aims: 1) to evaluate the effect of PKM? inhibition in the development and expression of cocaine behavioral sensitization. We will use a behavioral sensitization paradigm with intra VTA and intra NAc microinfusions of ZIP (PKM? selective inhibitor) at different stages of the sensitization process to determine PKM? 's role in the development and expression of behavioral sensitization. The hypothesize is that ZIP administration in the VTA and NAc will block the development and expression of cocaine sensitization 2) To determine the role of PKM? inhibition on AMPA currents and AMPA/NMDA ratios in VTA DA and NAc medium spiny neurons after cocaine sensitization. Using whole cell recordings from VTA DA and NAc medium spiny neurons, we will measure AMPA mediated EPSCs and AMPA/NMDA ratios from rats repeatedly exposed to cocaine. ZIP will be used to assess whether PKM? is necessary for the maintenance of the cocaine-induced potentiation. We hypothesize that ZIP will induce a decrease in AMPA currents and therefore, will diminish AMPA/NMDA ratios to basal levels in cocaine sensitized animals. 3) To assess the cellular substrate by which the PKM? inhibitor exerts its effects on addiction related plasticity. Using western blot analysis we will measure PKM and AMPA receptor subunit levels in the VTA and NAc during development and expression of cocaine sensitization. Second, we will use microinjections of the synthetic peptide Tat-GluR23y and rectification index curves in whole cell patch recordings to examine the contribution of GluR2-dependent and GluR2-lacking AMPA receptors in maintaining PKM? effects in cocaine sensitization. The hypothesis is that cocaine sensitization involves an increase in PKM? levels which is acting by inhibiting GluR2-dependent AMPA receptor removal from postsynaptic sites. This research will provide a better fundamental understanding of drug-induced plasticities in the CNS and might present possible avenues for therapeutic pharmacological interventions.